Answers

2016-03-19T20:53:27+05:30
Because helium , neon n argon have a completely filled outer shell n thus require no 
extra electrons. this is also the reason why they were discovered so late.
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2016-03-19T21:03:27+05:30
Element configuration
K L M N
2. 8. 8. 2.
helium. 2
Neon. 2. 8.
Argon. 2. 8. 8.
now here these elements have completely filled shells..
they don't need any more electron that's why there valence is zero....
0
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